The ability to image through obscuring media remains a problem in a variety of fields. By way of example, imaging of distant objects through the obscuring media of smoke or clouds is a problem that plagues satellite imaging analysts, firefighters, drivers, oceanographers, astronomers, military personnel, and medical personnel. The ability to improve resolution in each of these exemplary instances represents an opportunity to derive more information from images and presumably the decisions made from such images. By way of example, improved resolution in x-ray or endoscopy medical imagery facilitates lower radiation dosing and diagnosis of abnormal morphologies earlier than currently possible with conventional imaging methodologies. Conventional imaging techniques have, to a large extent, arrived at the theoretical limits of image resolution owing to wavelength-limited resolution, optical element distortions, and the reflective interaction between photons and an object to be imaged.
Ghost imaging holds the prospect of improving image resolution but efforts in regard to ghost imaging have met with limited success owing to a lack of understanding of the phenomena.
Currently, quantum ghost imaging is largely dependent on the transmission of electromagnetic waves (photons) through the object to be imaged. However, in most real world applications, photonic transmission is impractical, and instead of object light reflection is the basis of image formation. Even in transmissive imaging such as x-ray imaging considerable image information occurs through consideration of reflection. Additionally, other objects can best be imaged using the fluorescence of the object when illuminated by an external light source.
The first two-photon imaging experiment was reported by Pittman et al. in “Optical Imaging by Means of Two-photon Quantum Entanglement,” Physical Review A, Vol. 52, No. 5, November 1995. According to the article, a two-photon optical imaging experiment was performed based on the quantum nature of the signal and idler photon pairs produced in spontaneous parametric down-conversion. An aperture placed in front of a fixed detector was illuminated by a signal beam through a convex lens. A sharp magnified image of the aperture was found in the coincidence counting rate when a mobile detector is scanned in the transverse plane of the idler beam at a specific distance in relation to the lens. The experiment was named “ghost imaging” due to its surprising nonlocal feature, although the original purpose of the experiment was to study and to test the two-particle EPR correlation in position and in momentum for an entangled two-photon system. The experiments of ghost imaging in Pittman, et al. “Optical Imaging by Means of Two-Photon Entanglement,” Phys. Rev. A, Rapid Comm., Vol. 52, R3429 (1995) and ghost interference by Strekalov, et al, “Observation of Two-Photon ‘Ghost’ Interference and Diffraction,” Phys. Rev. Lett., Vol. 74, 3600 (1995) together stimulated the foundation of quantum imaging in terms of multi-photon geometrical and physical optics. The prior art transmissive ghost imaging optical scheme using entangled photons of Pittman et al. is depicted in FIG. 1.
This experiment was inspired by the theoretical work reported by Klyshko in Usp. Fiz. Nauk 154 133, Sov. Phys. Usp. 31, 74 (1988); Phys. Lett. A 132299 (1988) suggesting a non-classical two-photon interaction could exist. The Pittman experiment was immediately named “ghost imaging” due to its surprising nonlocal feature. The important physics demonstrated in that experiment, nevertheless, may not be the “ghost”. Indeed, the original purpose of the Pittman experiment was to study and to test the two-particle entanglement as originally detailed by Albert Einstein et al. (Einstein, Podolsky, Rosen) in Phys. Rev. 35 777 (1935) to determine if there was a correlation in position and in momentum for an entangled two-photon system. D'Angelo and colleagues in Phys. Rev. A 72, 013810 (2005) showed that ghost images produced by separable sources are subject to the standard statistical limitations. However, entangled states offer the possibility of overcoming such limitations to yield images that can achieve the fundamental limit through the high spatial resolution and nonlocal behavior of entangled systems.
Boto and colleagues in Phys. Rev. Lett. 85 2733 (2000) later developed an entangled multi-photon systems for sub-diffraction-limited imaging lithography and proposed a heuristic multiphoton absorption rate of a “noon” state and proved that the entangled N-photon system may improve the spatial resolution of an imaging system by a factor of N, despite the Rayleigh diffraction limit. The working principle of quantum lithography was experimentally demonstrated by D'Angelo et al. in 2001 by taking advantage of an entangled two-photon state of spontaneous parametric down-conversion as described in Phys. Rev. Lett. 87 013603.
Quantum imaging has so far demonstrated two peculiar features: (1) reproducing ghost images in a “nonlocal” manner, and (2) enhancing the spatial resolution of imaging beyond the diffraction limit. Both the nonlocal behavior observed in the ghost imaging experiment and the apparent violation of the uncertainty principle explored in the quantum lithography experiment are due to the two-photon coherent effect of entangled states, which involves the superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event in the quantum theory of photodetection as articulated by Glauber in Phys. Rev. 130 2529 (1963); and Phys. Rev. 131 2766 (1963). The nonlocal superposition of two-photon states may never be understood classically. Classical attempts, however, have never stopped in the history of EPR studies as evidenced by Bennink et al., who demonstrated 2002 by experiment, two co-rotated laser beams produced a projection shadow of an object mask through coincidence measurements as published in Phys. Rev. Lett. 89 113601 (2002). Instead of having a superposition of a large number of two-photon amplitudes, Bennink et al. used two correlated laser beams (imagine two back to back lasers) to simulate each two-photon amplitude one at a time. If the laser beam in the object arm is blocked by the mask at a certain rotating angle, there would be no coincidence in that angle and consequently defines a corresponding “position” in the nonlocal “image” plane. The block-unblock of the correlated laser beams thus projects a shadow of the object mask in coincidences. Interestingly, this experiment has excited a number of discussions concerning certain historical realistic models of EPR (Einstein, Podolsky, Rosen). Apparently, Bennink et al. have provided experimental evidence to support the concept of classical physical reality. Perhaps, the use of a transmitting mask as the object aperture function in the historical ghost imaging experiments may have been a factor responsible for this confused wrong idea.
The classical argument seems to get more support from thermal light ghost imaging, because thermal light itself is considered as classical. Thermal light ghost imaging was proposed in 2004 by Gatti et al. in Phys. Rev. A 70 013802, Wang and co-workers in quant-ph/0404078 and quant-ph/0407065, and Cai and Zhu in Phys. Rev. E 71 056607.
Thermal light ghost imaging for thermalized photons with a single CCD camera was used by Gatti et al. The main purpose was to simulate the two-photon correlation of entangled states by a classical source. In fact, two-photon correlation of thermal radiation is not a new observation. Hanbury-Brown and Twiss (HBT) demonstrated the second-order correlation of thermal light spatially (transverse) and temporally (longitudinal) in 1956 as published in Nature 177 28, and Nature 178 1046, and Nature 178 1447. Differing from entangled states, the correlation in chaotic radiation is only “partial”, which means 50% visibility at most. Nevertheless, chaotic light is a useful candidate for ghost imaging in certain applications. Recently, a number of experiments successfully demonstrated certain interesting features of ghost imaging by using chaotic light. Representative of these experiments using chaotic light are those by A. Valencia and colleagues in Phys. Rev. Lett. 94 063601 (2005); Scarcelli and colleagues in Phys. Rev. Lett. 96 063602 (2006); Ferri and colleagues in Phys. Rev. Lett. 94 183602 (2005); and Zhang and colleagues in Opt. Lett. 30 2354 (2005). A prior art transmissive ghost imaging optical scheme using thermalized photons Meyers/Deacon “Quantum Ghost Imaging Experiments,” SPIE Proceedings Vol. 6305 (2006) is depicted in FIG. 2.
The HBT experiment was successfully interpreted as statistical correlation of intensity fluctuations instead of two-photon coherence. A question about two-photon ghost imaging is then naturally raised: is the physics behind ghost imaging phenomenon a classical correlation of intensity fluctuations too? To answer this question, Scarcelli et al. in Phys. Rev. Lett. 96 063602 (2006) demonstrated a near-field ghost imaging of chaotic radiation. FIG. 3 is a prior art optical scheme for these experiments. In this work, Scarcelli et al. pointed out that (1) the classical interpretation leads to non-physical conclusions in the case of entangled two-photon ghost imaging; and (2) even if the classical interpretation may work for HBT, it will not work for the near-field ghost imaging of chaotic radiation. HBT correlation is measured in far-field, which is essentially a momentum-momentum self-correlation of a radiation mode. In the Scarcelli et al. experimental setup, however, the measurement is in near-field. In the near-field, for each position on the detection plane, a point photodetector receives a large number of modes in the measurement. The classical interpretation of statistical correlation of intensity fluctuations will not work in this experimental setup, as we know that different modes of chaotic light fluctuate randomly and independently. The fluctuations will cancel each other if more than one mode is involved in the measurement. On the other hand, Scarcelli et al. proved a successful alternative interpretation in terms of two-photon interference.
The experiment of Scarcelli et al. published in Phys. Rev. Lett. 98 039302 (2007) that builds on the earlier work of this group detailed above has not been able to convince Gatti et al. that ghost imaging is quantum in nature as evidenced by the publication of Gatti et al. in Phys. Rev. Lett. 98 039301. This ongoing lack of theoretical understanding of ghost imaging has hampered efforts to develop reflective ghost imaging systems for practical field uses in such fields as satellite, field, medical and research imaging.
Thus, there exists a need for a ghost imaging that is not dependent on the transmission properties of the object. Furthermore, there is a need for ghost imaging the multi-spectral properties of an object. An additional need exists for an imaging system that is tolerant of the scattering and distortion of an image as photons propagate through a distortion medium.
Ghost imaging in the prior art was dependent upon the transmission properties of an object. Accordingly, there exists a need for image creation where the transmission of light through the object is not possible or advantageous, such as when the object is opaque. Thus, there exists a need for an imaging system wherein light can be reflected from an object for subsequent image transmission.
In conventional image generation systems, a sufficient bandwidth necessary to transmit an image. There exists a need for image generation whereby the image can be generated and transmitted using minimal bandwidth, such as for example, using voltage detection readings.
Generally speaking, for the two dimensional (2D) images, there are two major graphic types: bitmap and vector image graphics. Three dimensional (3D) images are similarly formed with more complicated positional information relating to the third dimension.
A bitmap (or pixmap) image file format contains spatial information as to the location of the pixel or “bites” within the image or picture being transmitted. The term bitmap is derived from a mapped array of bits, and bitmapped and pixmap refer to the similar concept of a spatially mapped array of pixels. Both bitmapped and pixmapped formats contain spatial information. Raster graphics is the representation of images as an array of pixels.
Vector graphics are computer images that are stored and displayed in terms of vectors rather than points. Vector graphics utilizes, inter alia, points, lines, curves, and shapes or polygon(s), which are all based upon mathematical equations, to represent images in computer graphics.
Both bitmap and vector images utilize spatial information. A feature of a preferred embodiment of the present invention enables the transmission of an image without spatial information. As used herein the terminology “without spatial information” is defined as without positional information (such as that found in bitmap or pix map), or vector information such as that found in vector imaging.